Most of these CHDs need a multistep treatment strategy. Some of them (such as hypoplastic left heart syndrome) require a special therapy.
When the patient is born with single ventricle (classic C.D. of this pathology) and stenosis or pulmonary atresia that hinder pulmonary flow, in order to maintain a proper oxygenation, a prompt modified Blalock-Taussig anastomosis should be performed with a prosthesis tube of 4 mm between the subclavian artery and the homolateral pulmonary branch, usually on the left side.
If there is no pulmonary stenosis, a banding of the pulmonary artery to narrow the lumen, to limit the flow and the pressure transmitted to the pulmonary circuit, should be performed. This prevents the development of pulmonary hypertension that would prevent the patient from being well enough to undergo further surgical treatment.
A fenestrated asymmetric intracardiac device serves to do a total cavopulmonary anastomosis through cardiac catheterization. More particularly such an intracardiac device is used in pediatric cardiologic operations, more specifically to correct specific congenital heart disease in hemodynamic operations.
There are different congenital heart diseases (C.D.) with only one working ventricle available, so this disability necessitates a therapeutic strategy which allows the development of a special hemodynamic model. These cases are present in newborns with this cardiac malformation and it is absolutely necessary to correct it by means of surgery.
During the last decades different techniques have been introduced for the multistep preparation of the circulatory system, with the final aim of connecting the venous blood that comes from the heart through the superior and inferior vena cava with the pulmonary circuit, allowing oxygenation of blood. This involves performing a bypass to the right ventricle, because the non-existence or rudimentary structure of this C.D. does not allow one to perform its pump function of pulmonary circulation.
The goal is to maintain blood flow through a minor circuit with the pumping function of the only active ventricle. This circuit should have low resistance to flow, without obstruction sites, so that blood can flow properly, even if it is pumped with unnatural right heart venous pathways.
Under any of the two conditions described above, at the age of 6 or 8 months, patients should be subjected to a Bidirectional Glenn procedure. This procedure consists of the separation of the superior vena cava (SVC) from the right atrium (RA) and its connection with the right pulmonary branch (RPB). This way all the venous flow of the superior half of the body will flow directly to the pulmonary artery (PA) to become oxygenated without passing through the heart. This procedure is performed at this age because the head and the superior half of the body represent the 55% of the venous return. This is an open-heart procedure with cardiopulmonary bypass (CB).
The last step is to complete the total cavopulmonary connection (TCPC) at the age of 3 or 4 years old, by connecting the inferior vena cava to the pulmonary artery, also under cardiopulmonary bypass (CB). The surgical techniques have been substantially modified in the last decades, specially in this phase. Since the early Fontan-Kreutzer procedure, which consisted of joining the right atrium to the right pulmonary branch (atriopulmonary anastomosis) up to the current anastomosis with extracardiac tube between SVC and PA, several techniques have been tried.
This last-mentioned technique consists of the anastomosis of the inferior vena cava (IVC) to the right pulmonary branch (RPB) with the interposition of a Gore-Tex™ extracardiac prosthesis tube with a fenestration or hole in the RA as “discharge” in order to secure the postoperative cardiac output.
At this phase, the so-called “total cavopulmonary connection” (TCPC) is finished. Of late, some attempts have been made using a covered stent with a surgical catheterization to finish this last phase, and so avoid a new surgery, simplify the technique, minimize the risks as well as side effects.
These stents have an expandable tubular mesh made of different materials, such as a platinum-iridium, nickel-titanium, stainless-steel mesh and covered with an impermeable polymer, like expanded polytetrafluorothyelene (PTFE). With these devices, after performing the Bidirectional Glenn procedure, IVC is connected to SVC. The TCPC procedure with extracardiac tube as well as the procedure with the current stents have the inconvenience of supplying an unbalanced flow to the pulmonary circulation. Current stents have one or several fenestrations which allow discharge of blood from the circuit, if the hemodynamic condition is not ideal, allowing a right to left shunt at atrial level, so as to maintain the postoperative cardiac output. These openings or holes need to be closed or sealed when the patient's hemodynamic condition allows one to do so.
To show a better reference frame of the former state of the art, before this invention, FIG. 1 shows schematically a heart which suffers from these CHDs, before the Glenn procedure, and in FIG. 2 this same heart after the Glenn procedure.
The following acronyms are used in both figures:
RPA Right pulmonary artery
LPA Left pulmonary artery
SVC Superior vena cava
IVC Inferior vena cava
SHV Hepatic vein
Ra Right appendage
RA Right atrium
TV Tricuspid valve
The following are bibliographical references of these known more recent techniques:
“Surgical Preconditioning and Completion of Total Cavopulmonary Connection by Interventional Cardiac Catheterization: A New Concept,” (Heart 1996; 75: 403-409).
Through this technique the field to complete by catheterization the total cavopulmonary connection of high risk patients is carried out during the Glenn procedure.
A left banding is done between RA and SVC, setting a Gore-Tex™ tube with 3 to 7 perforations (multifenestrated) inside RA. During the next intervention, the banding is dilated with or without a Palmaz stent between SVC-AD, and the fenestrations are closed with Rashkind devices of 17 mm, used for the closure of the patent ductus arteriosus. If it is not possible to perform this technique, a covered stent inside a Gore-Tex™ tube is installed.
“A Novel Technique for Establishing Total Cavopulmonary Connection: From Surgical Preconditioning to Intervention Completion,” (J. Thorc Cardiovasc Surg. 2000; 120; 1007-9).
This technique contemplates the experimental use of a cavo-caval anastomosis with a covered stent through cardiac catheterization. Previously, a side-to-end anastomosis between SVC and distal RPB with PTFE should be performed. SVC is left banded in its joint with RA. The next procedure is to introduce endovascularly a stent graft from the right internal jugular vein, fitting it through the SVC banding, between SVC-RPA joint and IVC over the hepatic vena end. Then the pulmonary cava-cava artery anastomosis is completed.
“Effect of Baffle Fenestration on outcome of the Modified Fontan Operation,” (Circulation 1992; 86:1762-1769).
This technique shows the benefits of fenestration in the Fontan procedure in patients at high risk. This study compares a group of 91 patients in which a fenestration of 4 mm has been left in the intracardiac tube with 56 patients without fenestration. It was concluded that the fenestrated tube is associated with low mortality, less incidence of pleural effusion and less days in hospital.
Up to today none of these operation has shown optimal outcomes because in the long term a number of patients need different operations.
From the age of 6 approximately, the percentage of systemic venous return, which is kept up to the adult age, is reached. The 35% of the pulmonary flow of a healthy adult without C.D. is supplied by SVC and the 65% by IVC. The right lung, anatomically bigger, should receive approximately 55% of blood and the left lung, smaller, 45%. This implies a flow division from the IVC in 20% of the total (30.7% flow from IVC) that should run to the RPA, while the 45% left runs to the LPA.
With the C.D. corrective techniques currently known, it is not always feasible to guarantee a proper division of the pulmonary blood flow, resulting in a deficient supply according to the technique used in one or the other lung, usually the left one.
Another problem of the known corrective techniques with the devices mentioned above and which can result in serious inconveniences is the IVC transverse section in the grown up children which has an average of 18-20 mm, while the PA has an average diameter of 10-13 mm approximately. The known techniques and devices resolve this problem by connecting with a suture the upper end of the extracardiac conduit to the PA, and flattening it, which transforms a theoretically round section into a theoretically elliptical transverse section, resulting in an area decrease, and so increasing the flow resistance, if the speed of blood flow is reasonably constant.
The last problem is the longitudinal dimensions in case the device is intracardiac, because not all the patient's anatomies have the same dimensions and so the device should be adapted to the somatic growth.